Studies are underway regarding secondary batteries used in portable electronic devices and hybrid vehicles. As typical secondary batteries, lead storage batteries, alkali storage batteries, lithium ion batteries, and the like are known. Among a variety of secondary batteries, lithium secondary batteries in which a lithium ion battery is used have advantages of high output, high energy density, and the like.
As a cathode material used for lithium ion batteries, phosphate which includes Li and transition metals and have an olivine structure is known (for example, refer to Japanese Laid-open Patent Publication (Translation of PCT Application) No. 2000-509193). As a method for producing phosphate described above, a production method by a synthesis method (hydrothermal synthesis method) in which a hydrothermal reaction is used is known (for example, refer to Japanese Laid-open Patent Publication No. 2004-95385). When the hydrothermal synthesis reaction described in Japanese Laid-open Patent Publication No. 2004-95385 is used, it is possible to easily synthesize particles having aligned directions of the crystal growth of the obtained phosphate, and it also becomes possible to control the particle diameter and the particle shape.